The invention is directed to a method for producing a pharmaceutical piston stopper made substantially from rubber or a similar elastomer, which has a receiving cavity for connecting with a piston rod or a similar displacement transferring element and a piston section enclosed in a cap-like manner by a fluorinated polymer film or similar inert film. The piston section in the working position faces the contents of a syringe or carpule cylinder and abuts on the outer circumference with its inert film against the syringe or carpule cylinder. The piston stopper has an uncoated sealing section adjacent to this piston section which in the working position abuts against the syringe or carpule cylinder. In a forming operation a layered arrangement comprising a non-vulcanized rubber sheet and a fluorinated polymer film or a similar inert film is placed into a forming tool and is formed into a piston stopper under the influence of pressure and heat, whereby the rubber sheet is vulcanized and joined with the inert film in a non-detachable manner.
In addition, the invention is directed to a device to produce pharmaceutical piston stoppers made substantially from rubber or a similar elastomer, which have a receiving cavity for connecting with a piston rod or a similar displacement transferring element and a piston section which, in the working position, faces the contents of a syringe or carpule cylinder and is enveloped in a cap-like manner by a fluorinated polymer film or a similar inert film. The piston section, which may have a conical shape and/or a substantially flat face, abuts on the outer circumference with its inert film against the syringe or carpule cylinder. The piston stopper has adjacent to this piston section an uncoated sealing section which, along with an entire edge region of the inert film, flatly abuts in the working position against the syringe or carpule cylinder. A forming tool forms the piston stopper from a layered arrangement comprising a non-vulcanized rubber sheet and a fluorinated polymer film or a similar inert film, wherein the forming tool has at least one first die plate and a second die plate interacting with the former, which can be displaced relative to one another into closed and open positions. A blanking device separates the piston stoppers from a layered arrangement flange laterally projecting beyond the piston stoppers and remaining in the region of the partition plane of the forming tool.
The invention is further directed to a pharmaceutical piston stopper, which has a base body made from rubber or a similar elastomer, a receiving cavity within the base body for connecting a piston rod or a similar displacement transferring element and a piston section proximate a first end of the base body enveloped by a fluorinated polymer film or similar inert film. The piston section, in the working position, faces the contents of a syringe or carpule cylinder and abuts with its inert film on the outer circumference against the syringe or carpule cylinder. The piston stopper has an uncoated sealing section proximate a second end of the base body and adjacent to this piston section, the uncoated sealing section abutting in the working position against the syringe or carpule cylinder, and has at least one continuous sealing lip on its outer circumference.
When storing medications or pharmaceutical preparations, as a rule in liquid or powdery form, in the pre-filled syringe or carpule cylinders, varying requirements are placed on the piston stoppers to be used. Thus, a chemical or biological compatibility with the contents of the syringe or carpule cylinder is required, which on the one hand means that the substances contained in the material of the piston stopper must not leach into the medication situated in the syringe or carpule cylinder and contaminate it or alter its therapeutical effect. On the other hand, however, no active substances of the medication must penetrate into the piston stopper, because with increasing storage periods the concentration of the active substance in the medication would decrease. Finally, substances that penetrate from the medication into the piston stopper may also alter the functional properties of the piston stopper. Moreover, the piston stopper must seal the interior of the syringe or carpule cylinder against gas, liquid and germs.
From European published patent application EP 0 148 426 A1, a piston stopper made substantially from rubber is already known, which has a piston section which in the working position faces the contents of the syringe cylinder and is enveloped in a cap-like manner by an inert film and on its outer circumference has a continuous sealing lip coated with the inert film and abutting against the syringe cylinder. In this manner, the inert film should prevent a direct contact between the contents of the syringe cylinder and the rubber material that is incompatible with it. For the purpose of improving the sealing of the piston stopper against the syringe cylinder, adjacent to the coated piston section the piston stopper has a non-coated sealing section, which on its outer circumference has two parallel continuous sealing lips. In the working position these non-coated sealing lips abut against the syringe cylinder. Between the two sealing lips of the sealing section and between the uncoated piston section and the sealing lip of the sealing section adjacent to it a recess is respectively provided, by which the sealing lips are spaced from one another.
However, for pre-filled syringe systems, wherein the medication is stored in the syringe for a longer period, the piston stoppers are only conditionally suitable. The first sealing lip coated with the inert film seals only relatively poorly against the syringe cylinder. Due to this, it is possible that a portion of the medication in the syringe cylinder could leach through, between the first sealing lip and the wall of the syringe cylinder, into the recess situated between the first and the second sealing lip. During the administration of the medication this portion of the medication remains unused between the lamellae, as a result of which, for a syringe pre-filled with a specific quantity of a medication, the quantity of medication applied is correspondingly reduced. Moreover, the portion of the medication penetrated between the sealing lips of the piston stopper also comes into contact with the non-coated rubber material of the piston stopper, due to which the storage life of the medicinal contents of the syringe may be reduced.
The production of the known piston stopper is carried out in several operations. In the first operation for forming a first piston stopper portion with a piston section enveloped in a cap-like manner by the inert film, a non-vulcanized rubber sheet together with an inert film is pressed into a first hollow form of a caliper plate of a forming tool. There, the rubber sheet is vulcanized under the influence of pressure and heat and is non-detachably joined with the inert film. In a further operation the piston stopper portion thus formed is removed from the forming tool and blanked out from the coated rubber sheet. By doing so, the blanked out edge of the completed piston stopper forms the recess between the first sealing lip coated with the inert film and the second sealing lip adjacent to it. In a further operation the first piston stopper portion produced in this manner is placed into a hollow form of a second forming tool. Into this second forming tool a second non-vulcanized rubber sheet is placed, from which is formed, under the influence of pressure and heat, a second piston stopper portion, that is joined with the first piston stopper portion to provide the essentially complete piston stopper. During the forming in the second forming tool, a receiving cavity for connecting with the piston rod of a syringe is formed on the face of the piston stopper which is opposite to the inert film terminating at a spacing from the first piston stopper portion. Afterwards, the piston stopper is blanked out from the second rubber sheet.
The known method has the disadvantage that two forming operations and two blanking operations are necessary for the production of the piston stopper. Therefore, the method is relatively expensive. The method is also only conditionally suitable for a mass production. Although a plurality of the first piston stopper portions can be simultaneously formed in the first forming tool, they are, however, after their removal from the forming tool blanked out from the rubber sheet and then separated. The placing of the single piston stopper portions into a second forming tool, which has a number of forming cavities corresponding with the number of the piston stopper portions produced by the first forming tool, is therefore relatively complicated.